Microcomputer having processor capable of changing endian based on endian information in memory

Abstract

There is a need to provide a microcomputer capable of eliminating an external terminal for endian selection. Flash memory includes a user boot area for storing a program executed in user boot mode and corresponding endian information and a user area for storing a program executed in user mode and corresponding endian information. A data transfer circuit reads endian information stored in the user boot area or the user area in accordance with operation mode and supplies the endian information to a CPU before reset release of the CPU. Accordingly, an external terminal for endian selection can be eliminated.

What is claimed is: 
     
       1. A microcomputer comprising:
 a processor capable of changing endianness, the processor using an endian specified by endian information, and when an internal reset is in a first state and a processor reset is in a second state, starting resetting of the endian being used; 
 a nonvolatile memory that stores the endian information; and 
 a data transfer circuit that reads the endian information stored in the nonvolatile memory and supplies the processor with the endian information when the processor reset is in the second state after the internal reset changes from the first state to a third state, wherein: 
 the processor starts operation on the endian specified by the endian information after the processor reset changes from the second state to a fourth state with the third state of the internal reset; 
 the nonvolatile memory includes a first region for storing a first program executed when an operation mode is a first operation mode and first endian information, and a second region for storing a second program executed when the operation mode is a second operation mode and second endian information; and 
 before the processor reset changes from the second state to the fourth state, the data transfer circuit
 reads the first endian information stored in the first region and supplies the first endian information to the processor when the operation mode is the first operation mode, and 
 reads the second endian information stored in the second region and supplies the second endian information to the processor when the operation mode is the second operation mode. 
 
 
     
     
       2. The microcomputer according to  claim 1 , wherein the data transfer circuit includes:
 a selection circuit that selects, when the operation mode is the first operation mode, a first address for storing the first endian information, and selects, when the operation mode is the second operation mode, a second address for storing the second endian information; and 
 a storage circuit that
 when the selection circuit selects the first address, stores the first endian information read from the first address and outputs the first endian information to the processor, and 
 when the selection circuit selects the second address, stores the second endian information read from the second address and outputs the second endian information to the processor. 
 
 
     
     
       3. The microcomputer according to  claim 1 ,
 wherein the data transfer circuit
 detects one of changes from the first region to the second region and from the second region to the first region by accessing the processor, and 
 when the change from the first region to the second region is detected, reads the second endian information stored in the second region, and supplies the second endian information to the processor, when 
 when the change from the second region to the first region is detected, reads the first endian information stored in the first region, and supplies the first endian information to the processor. 
 
 
     
     
       4. The microcomputer according to  claim 3 , wherein the data transfer circuit includes:
 a selection circuit that selects, when the change from the first region to the second region is detected, a second address for storing the second endian information, and selects, when the change from the second region to the first region is detected, a first address for storing the first endian information; and 
 a storage circuit that
 when the selection circuit selects the first address, stores the first endian information read from the first address and outputs the first endian information to the processor, and 
 when the selection circuit selects the second address, stores the second endian information read from the second address and outputs the second endian information to the processor. 
 
 
     
     
       5. The microcomputer according to  claim 1 , wherein the processor reset changes from the second state to the fourth state when operation of the data transfer circuit is finished. 
     
     
       6. The microcomputer according to  claim 1 , wherein the internal reset and the processor reset have the first state and the second state, respectively, when a system reset is input. 
     
     
       7. The microcomputer according to  claim 6 ,
 wherein after the internal reset changes to the third state from the first state, the data transfer circuit outputs an address specifying a location of the nonvolatile memory, and 
 the nonvolatile memory outputs the endian information stored in the location specified by the address. 
 
     
     
       8. The microcomputer according to  claim 1 , wherein the data transfer circuit starts operation when the internal reset changes to the third state from the first state. 
     
     
       9. The microcomputer according to  claim 1 , wherein the data transfer circuit includes a data storage circuit storing the endian information which is transferred from the nonvolatile memory and is supplied to the processor. 
     
     
       10. The microcomputer according to  claim 9 ,
 wherein before the data storage circuit stores the endian information, the data transfer circuit outputs an address specifying a location of the nonvolatile memory, and 
 the nonvolatile memory outputs the endian information stored in the location specified by the address.